The mortality rate of colorectal cancer is second only to lung cancer. One of the strategies to reduce human cancer is by chemoprevention. The objectives of this proposed research are to study colon carcinogenesis and the inhibition of colon carcinogenesis using a new colonoscopic model in rats. In the Phase I feasibility study the new model was developed and the optimal conditions were established for the colonoscopic study of chemically induced carcinogenesis. The latent period, incidence, number, size, location and progression of the colon tumors can be determined by weekly colonoscopy. Video camera-assisted colonoscopy can identify neoplasms earlier than normal colonoscopy, and record the data for documentation and further analysis. This Phase II research will further develop this model to be used in the investigation of two-stage carcinogenesis of colon cancer, the carcinogenicity of human fecal mutagens, the effects of inhibitors on the progression of colon carcinogenesis. An orthotopic transplantable colon tumor model will be developed for chemotherapeutic studies.